Projection type display apparatus and image display method

ABSTRACT

A projection type display apparatus includes illumination unit that emits a plurality of color lights having a predetermined polarization direction, a plurality of optical path adjustment units that totally reflect the plurality of color lights, respectively, a plurality of optical modulation units that modulates the plurality of color lights totally reflected by the plurality of optical path adjustment units, respectively, to emit a plurality of modulated color lights, a synthesis unit that emits the plurality of modulated color lights emitted from the optical modulation units in a same direction, and a correction unit that is arranged on an optical path between the illumination unit and the synthesis unit and that changes a polarization state of light that entered the correction unit to covert light incident on the synthesis unit into linearly polarized light.

TECHNICAL FIELD

The present invention relates to a projection type display apparatus andan image display method.

BACKGROUND ART

In recent years, there has been proposed a display apparatus that uses aplurality of display elements such as DMD (Digital Micromirror Device).The display apparatus, that uses the plurality of display elements,includes an optical synthesis optical system that is configured in whicha plurality of projection lights emitted from the respective displayelements are synthesized on the same optical axis, and projects thesynthesized projection light. For example, Patent Literature 1 disclosesa display apparatus that includes three DMDs as display elements, and across dichroic prism (hereinafter, referred to as XDP) as an opticalsynthesis optical system.

FIG. 1 is a diagram illustrating the configuration of the displayapparatus described in Patent Literature 1. Display apparatus 1000illustrated in FIG. 1 includes illumination optical system 100, lightseparation XDP 210, dichroic mirror 220, reflection mirrors 230 and 240,condenser lenses 250 and 260, three DMDs 300R, 300G, and 300B, three TIR(Total Internal Reflection) prisms 400R, 400G, and 400B, opticalsynthesis XDP 500, and projection lens 600.

A light exited from illumination optical system 100 is separated into ared light and the mixed light of green and blue at light separation XDP210. The red light enters TI prism 400R via reflection mirror 240 andcondenser lens 260. The mixed light of green and blue enters dichroicmirror 220 via reflection mirror 230 and condenser lens 250. At dichroicmirror 220, the mixed light of green and blue is separated into a greenlight and a blue light. The green light enters TIR prism 400G, and theblue light enters TIR prism 400B.

The lights respectively made incident on TIR prisms 400R, 400G, and 400Bare totally reflected respectively on first surfaces 402R, 402G, and402B, and respectively enter DMDs 300R, 300G, and 300B that eachcorrespond to TIR prisms 400R, 400G, and 400B.

Each of DMDs 300R, 300G and 300B has a plurality of micromirrorsarranged in a matrix in the image forming region and, by rotating eachmicromirror to change the reflection direction of light, modulates theincident light to emit the modulated light as image light. The imagelights respectively emitted from DMDs 300R, 300G, and 300B aretransmitted through TIR prisms 400R, 400G, and 400B that each correspondto DMDs 300R, 300G, and 300B to enter XDP 500.

XDP 500 has second surfaces 506 and 508 for transmitting or reflectingthe incident image lights of respective colors, and emits a plurality ofimage lights incident on second surfaces 506 and 508 in the samedirection to synthesize the image lights of respective colors. Thesynthesized image light is emitted from XDP 500 toward projection lens600, and is then projected to a screen (not illustrated) via projectionlens 600.

In XDP 500, S-polarized light or P-polarized light is reflected bysecond surfaces 506 and 508 while the other is transmitted throughsecond surfaces 506 and 508. Thus, in order to efficiently synthesizethe lights respectively emitted from DMDs 300R, 300G and 300B, thelights incident on second surfaces 506 and 508 are converted intoS-polarized lights or P-polarized lights.

Further, DMDs 300R, 300G, and 300B are arranged such that the long sideof the image forming region may be inclined by 45° to the side of thelight incident surface of XDP 500. Therefore, display apparatus 1000must be inclined by 45° from a horizontal direction to normally displaya projected image.

CITATION LIST Patent Literature

-   Patent Literature 1: JP2000-330072A

DISCLOSURE OF THE INVENTION Problems to be Solved

In image display apparatus 1000 described in Patent Literature 1, acumbersome operation in which the casing is inclined must be carried outonly when an image is projected.

On the other hand, if DMDs 300R, 300G, and 300B are arranged such thatthe long side of the image forming region is parallel to the side of thelight incident surface of XDP 500, the projected image can be displayedin a normal state without inclining the casing.

In this case, however, the lights should be entered into TIR prisms400R, 400G, and 400B from an angle of 45° to the incident surface of XDP500, and as a result, the lights are elliptically polarized during thetotal reflection of the lights on first surfaces 402R, 402G, and 402B ofTIR prisms 400R, 400G, and 400B. In such a case, the light incident onXDP 500 cannot be converted into S-polarized light or P-polarized light,and thus there has been a problem in which contrast or luminance of theprojected image is reduced.

An object of the present invention is to provide a display apparatus anda display method that can prevent a reduction in contrast of theprojected image.

Solution to Problem

A projection type display apparatus according to the present inventionincludes: an illumination unit that emits a plurality of color lightshaving a predetermined polarization direction; a plurality of opticalpath adjustment units that totally reflect the plurality of colorlights, respectively; a plurality of optical modulation units thatmodulates the plurality of color lights totally reflected by theplurality of optical path adjustment units, respectively, to emit aplurality of modulated color lights; a synthesis unit that emits theplurality of modulated color lights emitted from the optical modulationunits in a same direction; and a correction unit that is arranged on anoptical path between the illumination unit and the synthesis unit andthat changes a polarization state of light that entered the correctionunit to covert light that is incident on the synthesis unit into alinearly polarized light.

An image display method according to the present invention includes:emitting a plurality of color lights having a predetermined polarizationdirection; totally reflecting the plurality of color lights,respectively; modulating the plurality of totally reflected colorlights, respectively; emitting the plurality of modulated color lightsin a same direction to synthesize the plurality of color lights; andprojecting the synthesized light, wherein a polarization state of thelight is changed to convert light incident on a synthesis unit thatsynthesizes lights into a linearly polarized light prior to thesynthesis of the plurality of lights.

Effects of Invention

According to the present invention, a display apparatus that can preventa reduction in contrast of a projected image can be provided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 A diagram illustrating the configuration of display apparatus1000 according to the comparative example of the present invention.

FIG. 2 A diagram illustrating the arrangement of components according toa modified example of display apparatus 1000 illustrated in FIG. 1.

FIG. 3 A diagram illustrating a relationship between a polarizationdirection in which a light is S-polarized light or P-polarized lightwith respect to a first surface and the polarization direction of lightincident on the first surface in the modified example illustrated inFIG. 2.

FIG. 4 A diagram illustrating the configuration of display apparatus 1according to a first exemplary embodiment of the present invention.

FIG. 5 A diagram illustrating the configuration of TIR prism 40B.

FIG. 6 A diagram illustrating the detailed configuration of a part ofTIR prism 40B.

FIG. 7 A diagram illustrating the configuration of DMD 50B.

FIG. 8 A diagram illustrating the operation of micromirror 51.

FIG. 9 A diagram illustrating the relative arrangement of TIR prism 40B,DMD 50B, and XDP 60.

FIG. 10 A diagram illustrating the relative arrangement of TIR prism40B, DMD 50B, and XDP 60.

FIG. 11 A diagram illustrating a relationship between the polarizationdirection of light incident on TIR prism 40B and a polarizationdirection in which the light is S-polarized light or P-polarized lightwith respect to first surface 43B of TIR prism 40B.

FIG. 12 A diagram illustrating the polarization states of the lightincident on TIR prism 40B and image light exited from DMD 50B.

FIG. 13 A diagram illustrating the configuration of display apparatus 2according to a second exemplary embodiment of the present invention.

FIG. 14 A diagram illustrating the polarization states of light incidenton TIR prism 40B and image light emitted from DMD 50B in displayapparatus 2.

FIG. 15 A diagram illustrating the configuration of display apparatus 3according to a third exemplary embodiment of the present invention.

DESCRIPTION OF EMBODIMENT

Hereinafter, the exemplary embodiments of the present invention will bedescribed with reference to the accompanying drawings. Herein andthroughout the drawings, components having similar functions are denotedby similar reference signs, and thus repeated description thereof may beomitted. In addition, for simplicity, a light flux is indicated by astraight line throughout the drawings.

First, a mechanism by which light reflected on a TIR prism is convertedinto elliptic polarized light will be described.

FIG. 2 is a diagram illustrating the arrangement of DMD 300B, TIR prism400B, and XDP 500.

DMD 300B is installed in parallel with the incident surface of XDP 500.In other words, the rectangular image forming region of DMD 300B and theincident surface of XDP 500 are both parallel to a yz plane. TIR prism400B is provided between DMD 300B and XDP 500. TIR prism 400B isarranged so that incident light can enter DMD 300B from a directionroughly vertical to rotation axis 302 of micromirror 301 provided in therectangular image forming region of DMD 300B. In other words, theincident light is totally reflected on first surface 402B that is thetotal reflection surface of TIR prism 400B, and then exits from TIRprism 400B to enter DMD 300B. TIR prism 400B is arranged so that firstsurface 402B can gradually approach the rectangular image forming regionof DMD 300B. More specifically, first surface 402B is a slope withrespect to the rectangular image forming region of DMD 300B, and is aslope along the direction roughly vertical to rotation axis 302 ofmicromirror 301.

FIG. 3 is a diagram illustrating a relationship with the polarizationdirection of the light incident on first surface 402B of TIR prism 400Bin the arrangement illustrated in FIG. 2. When light is made incident onTIR prism 400B from an angle of 45° with respect to the incident surfaceof XDP 500, an incident surface, when the light enters TIR prism 400B,is a surface that forms an angle of 45° with respect to the incidentsurface of XDP 500. Accordingly, a direction parallel to or vertical tothe incident surface of TIR prism 400B does not match a directionparallel to or vertical to the incident surface of XDP 500, nor is lightthat is S-polarized light or P-polarized light with respect to secondsurface 506 of XDP 500 S-polarized light or P-polarized light respect tofirst surface 402B of TIR prism 400B. The light incident on TIR prism400B has a polarization direction in which the light becomes S-polarizedlight or P-polarized light with respect to second surface 506 of XDP500, and thus the incident light is light that includes S-polarizedlight component and P-polarized light component when the light entersfirst surface 402B of TIR prism 400B.

When the light including the S-polarized light component and theP-polarized light component is totally reflected, the polarization stateof the light is disturbed. Specifically, when the light is totallyreflected, a part of the energy of the light that entered the totalreflection surface slightly seeps to a medium that forms the totalreflection surface to generate an evanescent light. Since the energy ofthe evanescent light is propagated in a direction parallel to the totalreflection surface, a phenomenon referred to as a Goos-Hanchen shift inwhich the phase of the light is varied occurs. The amount of variationin phase due to Goos-Hanchen shift is different between the S-polarizedlight component and the P-polarized light component. Consequently, whenlinear polarized light including the S-polarized light component and theP-polarized light component is totally reflected, the linear polarizedlight changes to be an elliptic polarized light.

The arrangement of DMD 300B, TIR prism 400B, and XDP 500 and thepolarization direction when a blue light enters XDP 500 via TIR prism400B and DMD 300B has been described. It should be noted that the samedescription applies to a red light and a green light.

First Exemplary Embodiment

FIG. 4 is a diagram illustrating the configuration of display apparatus1 according to a first exemplary embodiment of the present invention.Display apparatus 1 includes light source 10, illumination opticalsystem 20, light separation optical system 30, TIR prisms 40R, 40G, and40B, DMDs 50R, 50G, and 50B, XDP 60, correction optical elements 70R,70G, and 70B, and projection optical system 80. Projection opticalsystem 80 is a projection unit that projects a light synthesized by XDP60. Projection optical system 80 magnifies the incident light to projectit to a screen that is not illustrated.

Light source 10 includes light source lamp 11 and reflector 12. Lightsource lamp 11 is, for example, a metal halide lamp or a high pressuremercury lamp, and there is no particular limitation on its type.Reflector 12 converts light that is emitted from light source lamp 12into nearly parallel light to emit it. The nearly parallel light emittedfrom light source 10 enters illumination optical system 20.

Illumination optical system 20 includes first lens array 21, second lensarray 22, polarization conversion element 23, and superimposed lens 24.Illumination optical system 20 generates the linear polarized light fromthe nearly parallel light emitted from light source 10.

Each of first lens array 21 and second lens array 22 includes manylenses arrayed in a matrix. First lens array 21 is configured to dividethe incident light into the same number of light fluxes as that of theincluded lenses, and is configured to form an image of each dividedlight flux near second lens array 22.

The light emitted from second lens array 22 enters polarizationconversion element 23 and is converted, by polarization conversionelement 23, into linear polarized light having a predeterminedpolarization direction.

The linear polarized light exited from polarization conversion element23 enters superimposed lens 24. Each light flux divided by first lensarray 21 is superimposed on DMDs 50R, 50G, and 50B by superimposed lens24.

Light separation optical system 30 separates the light from illuminationoptical system 20 into a plurality of lights having colors that aredifferent from each other. For example, light separation optical system30 includes first dichroic mirror 31 by which the blue light isreflected and through which light having wavelengths longer than that ofthe blue light is transmitted, and second dichroic mirror 32 by whichthe green light is reflected and through which light having a wavelengthlonger than that of the green light is transmitted. Light separationoptical system 30 may further include a reflection mirror to change anoptical path.

From among the lights emitted from illumination optical system 20, theblue light is reflected by first dichroic mirror 31, and the lighthaving wavelengths longer than that of the blue light is transmittedthrough first dichroic mirror 31 to enter second dichroic mirror 32.From among the lights incident on second dichroic mirror 32, the greenlight is reflected by second dichroic mirror 32, and the light (e.g.,red light) having wavelengths longer than that of the green light istransmitted through second dichroic mirror 32.

The blue light reflected by first dichroic mirror 31 enters TIR prism40B. The green light reflected by second dichroic mirror 32 is reflectedon reflection mirror 36 to enter TIR prism 40G. The red lighttransmitted through second dichroic mirror 32 is reflected by reflectionmirrors 33, 34, and 35 to enter TIR prism 40R.

Light source 10, illumination optical system 20, and light separationoptical system 30 are collectively referred to as illumination unit 25.Illumination unit 25 emits a plurality of color lights having apredetermined polarization direction.

TIR prisms 40R, 40G, and 40B are optical path adjustment units thatchange the optical path of the incident light. Specifically, TIR prisms40R, 40G, and 40B totally reflect the color lights from illuminationunit 25 to emit the lights toward DMDs 50R, 50G, and 50B. The colorlights modulated by the micromirrors of respective DMDs 50R, 50G, and50B are transmitted through TIR prisms 40R, 40G, and 40B to enter XDP60.

FIG. 5 is a diagram illustrating the configuration of TIR prism 40B.FIG. 5 illustrates TIR prism 40B and DMD 50B, and it should be notedthat the same description applies to TIR prisms 40R and 40G and DMDs 50Rand 50G.

TIR prism 40B illustrated in FIG. 5 includes prism 41B and prism 42B,and first surface 43B is formed between prism 41B and prism 42B by wayof an air gap. Since an interface, that is made of the air gap and thathas a different refractive index, is formed on first surface 43B, whenlight enters first surface 43B at an angle equal to or larger than acritical angle, the light is totally reflected. TIR prism 40B isarranged so that the angle of the light incident on first surface 43Bfrom illumination unit 25 can be equal to or larger than the criticalangle, so that the totally reflected light can enter DMD 50B to bemodulated by each micromirror of DMD 50B, and so that the lightreflected by each micromirror can enter first surface 40B at an anglesmaller than the critical angle. In other words, TIR prism 40B totallyreflects the light from illumination unit 25 to emit it toward DMD 50B,and transmits the light from DMD 50B to emit it toward XDP 60.

FIG. 6 is a diagram illustrating the detailed configuration of prism41B. FIG. 6 illustrates prism 41B, and it should be noted that the samedescription applies to prisms 41R and 41G included in TIR prisms 40R and40G. The inner angles of a triangle on the bottom surface of prism 41Bare respectively 33°, 50°, and 97°, the refractive index of a glass is1.517, and the angle of the light incident on first surface 43B is48.5°. In this case, the angle at which the light emitted from prism 41Benters DMD 50B is 24°.

Referring back to FIG. 4, description will be made.

DMD 50R, 50G, and 50B are optical modulation elements that arerespectively provided corresponding to TIR prisms 40R, 40G, and 40B andthat are configured to modulate the lights that are totally reflected onfirst surfaces 43R, 43G, and 43B of the corresponding TIR prisms 40R,40G, and 40B and that emit the lights. These optical modulation elementsare also referred to as optical modulation units.

FIG. 7 is a diagram illustrating the configuration of DMD 50B. FIG. 7illustrates DMD 50B, and it should be noted that the same descriptionapplies to DMDs 50R and 5G. DMD 50B includes a plurality of micromirrors51 arranged in a matrix, and each micromirror 51 corresponds to onepixel of a projected image. Each micromirror 51 is rotated aroundrotation axis 52 to change the angle of the incident light. Micromirror51 of DMD 50B is disposed so that rotation axis 52 is directed in thediagonal direction of square micromirror 51 and so that a planeincluding the incident light and the reflected light is orthogonal torotation axis 52.

FIG. 8 is a diagram illustrating the operation of micromirror 51. Acontrol unit that is not illustrated drives each micromirror 51according to a video signal to switch between an ON state in which themicromirror inclines in an incident direction of the light and an OFFstate in which the micromirror inclines in a direction opposite theincident direction. If it is presumed that a rotational angle when thereflection surfaces of the plurality of micromirrors 51 form one planeis set to 0°, each micromirror 51 inclines by ±12° around rotation axis52. In this case, if light of an incident angle 24° is reflected bymicromirror 51 of the ON state, the light travels in a normal directionof micromirror 51 when the rotational angle is 0°. If light of anincident angle 24° is reflected by micromirror 51 of the OFF state, thelight travels in a direction that makes an angle of 48° with a normaldirection of micromirror 51 when the rotational angle is 0°.

The ON-lights reflected by DMDs 50R, 50G and 50B are transmitted throughfirst surfaces 43R, 43G and 43B of TIR prisms 40R, 40G and 40B to besynthesized by XDP 60, and are then projected on the screen (notillustrated) or the like by the projection lens. The OFF-lights do notreach the screen because they are absorbed by optical absorbers that arearranged between DMDs 50R, 50G, and 50B and XDP 60. The luminance of apixel to which each micromirror 51 corresponds is changed by changingthe ratio between the time during which each micromirror 51 is in the ONstate and the time during which each micromirror 51 is in the OFF state.

In FIG. 4, XDP 60 is a synthesis unit that synthesizes the lightsrespectively exited from DMDs 50R, 50G and 50B by reflecting ortransmitting the lights by or through second surfaces 61 and 62 to emitthem in the same direction.

Specifically, green light that is P-polarized light is transmittedthrough second surfaces 61 and 62, red light that is S-polarized lightis reflected by second surface 61, and blue light that is an S-polarizedlight is reflected on second surface 62. However, even when illuminationunit 25 emits linear polarized light that is S-polarized light orP-polarized light to second surfaces 61 and 62, the polarization stateis disturbed during the reflection on the first surface of TIR prism 40to be converted to an elliptic polarized light.

FIGS. 9 and 10 are diagrams illustrating the relative arrangement of TIRprism 40B, DMD 50B, and XDP 60. DMD 50B and TIR prism 40B are arrangedso that rotation axis 52 provided in the diagonal direction of eachmicromirror 51 located in the image forming region of DMD 50B and aplane including incident light and reflected light are orthogonal toeach other. In addition, DMD 50B is disposed with respect to XDP 60 sothat the long side of the image forming region of DMD 50B and the sideof the upper surface of XDP 60 are parallel to each other. The lightenters TIR prism 40B at an angle of 45° to the incident surface of XDP60. Accordingly, the light totally reflected by first surface 43B of TIRprism 40B enters DMD 50 at the angle of 45° to the incident surface ofXDP 60.

FIG. 11 is a diagram illustrating a relationship between thepolarization direction of the light incident on TIR prism 40B and apolarization direction in which the light is S-polarized light orP-polarized light with respect to first surface 43B of TIR prism 40B. Inan example illustrated in FIG. 11, the light incident on TIR prism 40Bhas a polarization direction in which the light is P-polarized lightwith respect to second surfaces 61 and 62 of XDP 60. However, since thedirection of the slope of first surface 43B and the polarizationdirection of the incident light do not match nor intersect each other,the light incident on TIR prism 40B is light that includes anS-polarized light component and a P-polarized light component withrespect to first surface 43B.

FIG. 12 is a diagram illustrating the polarization states of the lightincident on TIR prism 40B and image light emitted from DMD 50B. Thelight incident on TIR prism 40B, which is linear polarized light that ispolarized in a direction parallel or vertical to the incident surface ofXDP 60, includes an S-polarized light component and a P-polarized lightcomponent with respect to first surface 43B. In this case, a phasechange of light, referred to as a Goos-Hanchen shift, occurs whentotally reflecting the light on first surface 40B. The amount of thisphase change is different between the S-polarized light component andthe P-polarized light component. For example, in the case of TIR prism40B having the configuration illustrated in FIG. 5 and FIG. 6, a phasechange that occurs on first surface 43B of TIR prism 40B is 56.4° at Spolarization, and 102.0° at P polarization. Thus, a relative phasedifference generated between the S-polarized light and the P-polarizedlight after totally reflecting the light is 45.6°. This relative phasedifference is equal to about a ⅛ wavelength.

In this way, when the inclination direction of the total reflectionsurface and the polarization direction of the linear polarized light donot match nor intersect each other, the linear polarized light reflectedon the total reflection surface becomes an elliptic polarized light.Accordingly, the light incident on DMD 50B from TIR prism 40B becomes anelliptic polarized light. Since the polarization state of the light doesnot change when the light is reflected on DMD 50B, the light modulatedby DMD 50B becomes an elliptic polarized light.

FIGS. 9 to 12 illustrate the arrangement of TIR prism 40B, DMD 50B, andXDP 60 through which the blue light is transmitted and the polarizationstate of the blue light, and it should be noted that the samedescription applies to the red light and the green light.

Correction optical elements 70R, 70G, and 70B illustrated in FIG. 4 area correction unit that is arranged on an optical path betweenillumination unit 25 and XDP 60 and that changes the polarization stateof the incident light to convert the light incident on XDP 60 intoS-polarized light or P-polarized light. Correction optical elements 70R,70G, and 70B are arranged on optical paths between respective TIR prisms40R, 40G, and 40B and XDP 60. Correction optical elements 70R, 70G, and70B correct lights that are modulated by DMDs 50R, 50G, and 50B and thatare respectively transmitted through TIR prisms 40R, 40B, and 40G to belinear polarized lights. XDP 60 is designed to synthesize, with respectto image lights emitted from DMDs 50R, 50G, and 50B, the respectivelights of the polarized light components of specific directions on thesame optical axis. Therefore, correction optical elements 70R, 70G, and70B correct the light incident on XDP 60 to be light polarized in thespecific direction. More specifically, correction optical elements 70R,70G, and 70B are provided for each color light emitted from illuminationunit 25, green color correction optical element 70G providedcorresponding to the green light converts the incident ellipticpolarized light into a P-polarized light, and red color correctionoptical element 70R and blue color correction optical element 70Bconvert the incident elliptic polarized lights into S-polarized lights.

The lights incident on correction optical elements 70R, 70G, and 70Bhave been totally reflected on first surfaces 43R, 43G, and 43B of TIRprisms 40R, 40G, and 40B to be changed from linear polarized lights toelliptic polarized lights. Correction optical elements 70R, 70G, and 70Bchange, for example, the phases of the S-polarized light component andthe P-polarized light component of the incident light so as to cancelthe relative phase difference between the S-polarized light componentand the P-polarized light component of the light that is generated whentotally reflecting the light by TIR prisms 40R, 40G, and 40B. In theconfiguration illustrated in FIGS. 4 to 12, correction optical elements70R, 70G, and 70B include at least one ⅛ wavelength plate (⅛ λ plate),and for example, correction optical elements 70R, 70G, and 70B are ⅛wavelength plates or ⅝ wavelength plates (⅝ λ plates). Green correctionoptical element 70G that corresponds to light that is transmittedthrough second surfaces 61 and 62 of XDP 60 is a ⅝ wavelength plate. Redcolor correction optical element 70R and blue color correction opticalelement 70B that correspond to lights that are reflected by secondsurfaces 61 and 62 of XDP 60 are ⅛ wavelength plates. Accordingly, thered image light is corrected from an elliptic polarized light to a lightpolarized in a direction vertical to the incident surface of XDP 60, thegreen image light is corrected from an elliptic polarized light to alight polarized in a direction parallel to the incident surface of XDP60, and the blue image light is corrected from an elliptic polarizedlight to a light polarized in the direction vertical to the incidentsurface of XDP 60. As a result, when entering first surface 61 or 62 ofXDP 60, the red and blue image lights are converted into S-polarizedlights while the green image light is converted into a P-polarizedlight.

For green light correction optical element 70G, in place of the ⅝wavelength plate, a ½ wavelength plate (½ λ plate) and a ⅛ wavelengthplate (⅛ λ plate) may be arrayed in a light traveling direction.Correction optical elements 70R, 70G, and 70B may be configured in anymanner as long as the lights that are transmitted through secondsurfaces 61 and 62 of XDP 60 are converted into P-polarized lights whilethe light that is reflected by second surface 61 and light that isreflected by second surface 62 are converted into S-polarized lights.

Modified Example

In the aforementioned embodiment, correction optical elements 70R, 70G,and 70B change the phases of the S-polarized light component and theP-polarized light component of the incident light so as to cancel therelative phase difference between the S-polarized light component andthe P-polarized light component of the light that is generated whentotally reflecting the light by TIR prisms 40R, 40G, and 40B. However,the present invention is not limited to this example. For example,correction optical elements 70R, 70G, and 70B may change thepolarization state of the incident light so as to cancel the light of apolarized light component other than the specific direction incident onXDP 60.

Specifically, correction optical elements 70R, 70G, and 70B include atleast one polarization plate. For example, red correction opticalelement 70R and blue correction optical element 70B that correspond tothe light incident on second surface 61 or 62 of XDP 60 may bepolarization plates. In this case, for green correction optical element70G that corresponds to light that is transmitted through secondsurfaces 61 and 62 of XDP 60, a polarization plate and a ½ wavelengthplate may be arrayed in this order in the light traveling direction. Thepolarization plate transmits only the light of a specific directionwhile absorbing or reflecting the light of the other polarizationdirection. The polarization plates used for correction optical elements70R, 70G, and 70B all have characteristics of transmitting the polarizedlight of a direction vertical to the incident surface of XDP 60.Accordingly, the light that is transmitted through the polarizationplate is converted into S-polarized light, and by further transmissionthrough the ½ wavelength plate, the green light is converted intoP-polarized light.

As described above, according to the first exemplary embodiment of thepresent invention, the plurality of color lights, that have thepredetermined polarization direction and that are emitted fromillumination unit 25, enters the plurality of TIR prisms 40R, 40G, and40B to be totally reflected. The totally reflected lights arerespectively modulated by DMDs 50R, 50G, and 50B that are providedcorresponding to TIR prisms 40R, 40G, and 40B. The respective lightsemitted from respective DMDs 50R, 50G, and 50B are synthesized by XDP 60to be emitted. Correction optical elements 70R, 70G, and 70B, whichchange the polarization state so that the light incident on XDP 60becomes S-polarized light or P-polarized light, are arranged on theoptical paths between illumination unit 25 and XDP 60. As a result, evenwhen the light is converted into an elliptic polarized light prior toentering XDP 60, since the light incident on XDP 60 can be convertedinto S-polarized light or P-polarized light, the generation of a straylight in XDP 60 can be prevented and a reduction in contrast of theprojected light can be prevented.

According to the present invention, correction optical elements 70R,70G, and 70B change the polarization state of the light so as to cancelthe phase difference between the S-polarized light component and theP-polarized light component of the light that is generated when totallyreflecting the light by TIR prisms 40R, 40G, and 40B. As a result, evenwhen a phase difference is generated between the S-polarized lightcomponent and the P-polarized light component during the totalreflection of the light on TIR prisms 40R, 40G, and 40B, since the phasedifference is cancelled, it is able to more surely prevent a reductionin contrast of the projected image. In addition, since a light that hasbeen a stray light can be used as a projection light by canceling thephase difference, the luminance of the projected image can be improved.

According to the present invention, correction optical elements 70R,70G, and 70B include at least one ⅛ wavelength plate. More specifically,XDP 60 reflects or transmits the respective color modulated lights toemit them in the same direction. In this case, correction opticalelements 70R, 70G, and 70B are provided corresponding to each light thatis incident on XDP 60, correction optical elements 70R and 70B thatcorrespond to the lights that are reflected on XDP 60 are ⅛ wavelengthplates, and correction optical element 70G that corresponds to the lightthat is transmitted through XDP 60 includes at least one ½ wavelengthplate. As a result, in the case where a phase difference equivalent to a⅛ wavelength is generated on reflection surfaces 43R, 43G, and 43B ofTIR prisms 40R, 40G, and 40B, a reduction in contrast of the projectedimage can be more reliably prevented and the luminance of the projectedimage can be increased.

According to the present invention, correction optical elements 70R,70G, and 70B are respectively provided on the optical paths between TIRprisms 40R, 40G, and 40B and XDP 60. As a result, since the light isconverted into linear polarized light in which the polarization state ofthe light has been converted immediately before its entry into XDP 60,the light incident on XDP 60 can be more reliably converted into linearpolarized light, and a reduction in contrast of the projected image canbe reduced.

Furthermore, according to the modified example of the embodiment,correction optical elements 70R, 70G, and 70B include at least onepolarization plate. More specifically, XDP 60 reflects or transmits therespective color modulated lights to emit them in the same direction. Inthis case, correction optical elements 70R, 70G, and 70B are providedcorresponding to each light that is incident on XDP 60, correctionoptical elements 70R and 70B that correspond to the lights that arereflected by XDP 60 are polarization plates, and correction opticalelement 70G that corresponds to the light that transmits through XDP 60includes a polarization plate and one ½ wavelength plate. Accordingly,from among the lights incident on XDP 60, the components other thanS-polarized light or P-polarized light polarized in the directionvertical or parallel to the incident surface of XDP 60 are reflected orabsorbed. As a result, a light that is a stray light in XDP 60 can bemore reliably reduced and a reduction in contrast of the projected imagecan be prevented.

Second Exemplary Embodiment

FIG. 13 is a diagram illustrating the configuration of display apparatus2 according to a second exemplary embodiment of the present invention.

Display apparatus 1 includes correction optical elements 70R, 70G, and70B that convert the lights into linear polarized lights after thepolarization state has been disturbed on TIR prisms 40R, 40G, and 40B,and correction optical elements 70R, 70G, and 70B are arranged betweenTIR prisms 40R, 40G, and 40B and XDP 60. On the other hand, displayapparatus 2 includes, in place of correction optical elements 70R, 70G,and 70B, correction optical elements 90R, 90G, and 90B that convertlights into elliptic polarized lights before entry into TIR prisms 40R,40G, and 40B so that the lights are totally reflected by TIR prisms 40R,40G, and 4B are of linear polarized lights.

Hereinafter, differences from display apparatus 1 will be described.

Display apparatus 2 includes correction optical elements 90 arranged onoptical paths between illumination unit 25 and TIR prisms 40R, 40G, and40B, for example, on optical paths between light separation opticalsystem 30 and TIR prisms 40R, 40G, and 40B. More specifically, displayapparatus 2 includes red correction optical element 90R that is providedbetween reflection mirror 35 and red TIR prism 40R, and green correctionoptical element 90G that is provided between second dichroic mirror 32and green TIR prism 40G. In addition, display apparatus 2 includes bluecorrection optical element 90B that is provided between first dichroicmirror 31 and blue TIR prism 40B.

Each of correction optical elements 90R, 90G, and 90B changes thepolarization state of incident light so that light incident on XDP 60becomes linear polarized light having a predetermined polarizationdirection. Specifically, correction optical elements 90R, 90G, and 90Bcorrect the polarization states of the lights in advance prior toentering TIR prisms 40R, 40G, and 40B so as to cancel a relative phasedifference generated between S-polarized light and P-polarized light ona total reflection surface.

As described above in the first embodiment, in the configurationillustrated in FIGS. 5 to 12, the relative phase difference that isapproximately equal to a ⅛ wavelength is generated between P-polarizedlight and S-polarized light. Correction optical elements 90R, 90G, and90B apply a phase difference reverse in sign but equal in size to thisrelative phase difference to linearly polarized illumination lightsprior to entering TIR prisms 40R, 40G, and 40B to convert the linearpolarized lights into elliptic polarized lights. For example, redcorrection optical element 90R and blue correction optical element 90Bare ⅛ wavelength plates, while green correction optical element 90G is a⅝ wavelength plate.

FIG. 14 is a diagram illustrating the polarization states of lightincident on TIR prism 40B and color light on the total reflectionsurface of TIR prism 40B in display apparatus 2. Color light that istransmitted through correction optical element 90B of display apparatus2 to enter TIR prism 40B is converted into an elliptic polarized light.When this elliptic polarized light is totally reflected by the totalreflection surface of TIR prism 40B, a Goos-Hanchen shift occurs,thereby causing changes in a phase. The amount of this phase changevaries between S-polarized light and P-polarized light. However, bycombining the amount of a phase change generated due to transmissionthrough correction optical element 90 with the amount of the phasechange generated due to the Goos-Hanchen shift, the change amount in thecase of S-polarized light and the change amount in the case ofP-polarized light are made approximately equal to each other, therebyreducing a relative phase difference.

Accordingly, light incident on DMD 50B is converted into linearpolarized light polarized in a direction parallel to the incidentsurface of XDP 60. Since the polarization state is not changed whilebeing reflected on DMD 50B, image light emitted from DMD 50B is alsoconverted into linear polarized light polarized in the directionparallel to the incident surface of XDP 60.

FIG. 14 illustrates the change in polarization state until the bluelight enters XDP 60 via TIR prism 40B and DMD 50B, and it should benoted that the same description applies to the red light and the greenlight.

Modified Example

In the aforementioned second embodiment, correction optical elements90R, 90G, and 90B, which are arranged between light separation opticalsystem 30 and respective TIR prisms 40R, 4G, and 40B, correct thepolarization states of the illumination lights immediately prior toentering respective TIR prisms 40R, 4G, and 40B. However, the presentinvention is not limited to this example. The arrangement and the numberof correction optical elements 90R, 90G, and 90B included in displayapparatus 2 may be set in any manner as long as light incident onprojection optical system 80 increases.

For example, in place of correction optical elements 90R, 90G, and 90B,one correction optical element may be installed between illuminationoptical system 20 and light separation optical system 30. In this case,since the rotational direction of polarized light changes on eachreflection surface, the number of reflection surfaces must be taken intoconsideration. In addition, in place of correction optical elements 90R,90G, and 90B, two correction optical elements may be installed betweenfirst dichroic mirror 31 and blue TIR prism 40B and between firstdichroic mirror 31 and second dichroic mirror 32, respectively.

For green light correction optical element 70G, in place of the ⅝wavelength plate, a ½ wavelength plate and a ⅛ wavelength plate may bearrayed in a light traveling direction.

As described above, according to the second embodiment of the presentinvention, correction optical elements 90R, 90G, and 90B are arranged onthe optical paths between illumination unit 25 and respective TIR prisms40R, 40G, and 40B. As in the aforementioned case, a reduction incontrast of a projected image can be prevented. Further, compared withthe case where the polarization states of the lights emitted from TIRprisms 40R, 40G, and 4B are corrected, the freedom in the arrangementand the number of correction optical elements can be increased, and thearrangement and the number of correction optical elements can beflexibly designed according to the design conditions of displayapparatus 2.

Third Exemplary Embodiment

FIG. 15 is a diagram illustrating the configuration of display apparatus3 according to a third exemplary embodiment of the present invention.

Illumination unit 25 in display apparatus 1 and display apparatus 2separates a white light into a plurality of color lights to use them asillumination lights for illuminating DMD 50. On the other hand,illumination unit 26 of display apparatus 3 uses color light emittedfrom each of a plurality of light sources as an illumination light.

Illumination unit 26 includes light sources 10R, 10G, and 10B that emitsred, green, and blue lights, respectively and illumination opticalsystems 20R, 20G, and 20B including conversion optical systems thatconvert the red, green, and blue lights into color illumination lightshaving predetermined polarization directions, respectively.

Each light source 10 includes light emitting element 13 that emits eachcolor light, and lens 14 that converts the color light emitted fromlight emitting element 13 into nearly parallel light. For example, lightsource 10R includes light emitting element 13R that emits a red light,and lens 14R that converts the color light emitted from light emittingelement 13R into nearly parallel light. Light emitting element 13 is,for example, a LED (Light Emitting Diode).

Illumination optical systems 20R, 20G, and 20B convert the incidentcolor lights into linear polarized lights for uniformly illuminatingDMDs 50R, 50G, and 50B. Illumination optical system 20R and illuminationoptical system 20B convert the incident color lights into linearpolarized lights polarized in a direction vertical to the incidentsurface of XDP 60, while illumination optical system 20G converts theincident color light into linear polarized light polarized in adirection parallel to the incident surface of XDP 60. The respectivelights emitted from respective illumination optical systems 20respectively enter TIR prisms 40R, 40G, and 40B.

As described above, according to the third embodiment of the presentinvention, illumination optical system 26 includes the plurality oflight sources 13R, 13G, and 13B for emitting the color lights. Thus, theluminance of a projected image can be improved because the plurality oflight sources is used, and the apparatus can be reduced in size becausea separation optical system for separating the white light into aplurality of color lights does not need to be provided. As a result,even in the configuration in which the luminance is improved and inwhich the apparatus is reduced in size, a reduction in contrast of theprojected image can be prevented.

The present invention has been described by way of exemplaryembodiments. However, the present invention is not limited to theaforementioned exemplary embodiments. Various changes understandable tothose skilled in the art can be made to the configuration and thespecifics of the present invention within the scope of the invention.

For example, in the first and second exemplary embodiments, light source10 includes light source lamp 11, and reflector 12 that converts thelight emitted from light source lamp 11 into the nearly parallel light.However, the present invention is not limited to this example. Forexample, by using a lens, the light emitted from light source lamp 11may be converted into nearly parallel light. In this case, a LED or aphosphor that absorbs exciting energy to radiate a fluorescent light canbe used as light source lamp 11.

In the aforementioned exemplary embodiment, illumination optical system20 adopts a configuration in which first lens array 21, second lensarray 22, polarization conversion element 23 and superimposed lens 24are used. However, the present invention is not limited to this example.For example, illumination optical system 20 may adopt a configurationsuch that a rod integrator is used.

In the aforementioned exemplary embodiment, superimposed lens 24 is asingle optical component. However, the present invention is not limitedto this example. For example, superimposed lens 24 may be a plurality oflenses or may adopt a configuration where a folding mirror is added inorder to improve the performance of illumination optical system 20 or inorder to adjust the size of the apparatus.

Furthermore, in the aforementioned exemplary embodiment, the arrangementof the correction optical elements in display apparatus 3 according tothe third exemplary embodiment is similar to that in display apparatus 1according to the first exemplary embodiment. However, the presentinvention is not limited to this example. For example, the arrangementof the correction optical elements in display apparatus 3 can be changedto be similar to that of the second embodiment.

EXPLANATION OF REFERENCE NUMBERS

-   -   1, 2, 3 Display apparatus    -   10 Light source    -   11 Light source lamp    -   12 Reflector    -   20 Illumination optical system    -   21 First lens array    -   22 Second lens array    -   23 Polarization conversion element    -   24 Superimposing lens    -   25, 26 Illumination unit    -   30 Light separation optical system (separation unit)    -   31 First dichroic mirror    -   32 Second dichroic mirror    -   33, 34, 35 Reflection mirror    -   40R, 40G, 40B TIR prism (optical path adjustment unit)    -   50R, 50G, 50B DMD (optical modulation unit)    -   60 XDP (synthesis unit)    -   70R, 70G, 70B Correction optical element (correction unit)    -   90R, 90G, 90B Correction optical element (correction unit)    -   80 Projection optical system (projection unit)

1. A projection type display apparatus comprising: an illumination unitthat emits a plurality of color lights having a predeterminedpolarization direction; a plurality of optical path adjustment unitsthat totally reflect the plurality of color lights, respectively; aplurality of optical modulation units that modulates the plurality ofcolor lights totally reflected by the plurality of optical pathadjustment units, respectively, to emit a plurality of modulated colorlights; a synthesis unit that emits the plurality of modulated colorlights emitted from the optical modulation units in a same direction;and a correction unit that is arranged on an optical path between theillumination unit and the synthesis unit and that changes a polarizationstate of light that entered the correction unit to covert light that isincident on the synthesis unit into linearly polarized light.
 2. Theprojection type display apparatus according to claim 1, wherein thecorrection unit changes the polarization state of the entered light tocancel a phase difference between an S-polarized light component and aP-polarized light component of light that is generated when light istotally reflected by the optical path adjustment unit.
 3. The projectiontype display apparatus according to claim 1, wherein the correction unitincludes at least one ⅛ wavelength plate.
 4. The projection type displayapparatus according to claim 3, wherein the synthesis unit reflects ortransmits each modulated color light to emit the light in the samedirection, wherein the correction unit includes a first correction unitthat is arranged to correspond to light that is reflected by thesynthesis unit and a second correction unit that is arranged tocorrespond to light that transmits through the synthesis unit, the firstcorrection unit being a ⅛ wavelength pate, the second correction unitincluding at least one ½ wavelength plate.
 5. The projection typedisplay apparatus according to claim 1, wherein the correction unitincludes at least one polarization plate.
 6. The projection type displayapparatus according to claim 5, wherein the synthesis unit reflects ortransmits each modulated color light to emit the light in the samedirection, wherein the correction unit includes a first correction unitthat is arranged to correspond to light that is reflected by thesynthesis unit and a second correction unit that is arranged tocorrespond to light that transmits through the synthesis unit, the firstcorrection unit being a first polarization plate, the second correctionunit including a second polarization plate and a ½ wavelength plate. 7.The projection type display apparatus according to claim 1, wherein thecorrection unit is provided on each optical path between the pluralityof optical path adjustment units and the synthesis unit.
 8. Theprojection type display apparatus according to claim 1, wherein thecorrection unit is provided on an optical path between the illuminationunit and the plurality of optical path adjustment units.
 9. An imagedisplay method comprising: emitting a plurality of color lights having apredetermined polarization direction; totally reflecting the pluralityof color lights, respectively; modulating the plurality of totallyreflected color lights, respectively; emitting the plurality ofmodulated color lights in a same direction to synthesize the pluralityof color lights; and projecting the synthesized light, wherein the imagedisplay method further includes, prior to the synthesis of the pluralityof modulated color lights, changing a polarization state of eachmodulated color light to convert the modulated color light into alinearly polarized light.